The organisms which produce .alpha.-glucosidase (.alpha.-D-glucoside glucohydrolase, EC 3.2.1.20) can be found widely in animals, plants, and microorganisms, and the .alpha.-glucosidases produced thereby show various characteristic properties depending on their source of origin. For example, the .alpha.-glucosidase originated from yeast is an enzyme scarcely affected by the sugar linked to non-reducing terminal glucose or aglycon of maltooligoglucoside derivatives as substrates, and is mainly used for the determination of .alpha.-amylase. The .alpha.-glucosidase in human urine or hog blood is known to scarcely show activity unless substrates have a glucose linked to non-reducing terminal glucose and said linkage is .alpha.-1,4-linkage.
With regard to the DNA sequence and the amino acid sequence of the .alpha.-glucosidase gene, there have been known those of human lysosomal .alpha.-glucosidase [Biochem. J. 272: 493-497 (1990)], fly .alpha.-glucosidase [J. Mol. Biol. 166 101-118 (1983)], mosquito .alpha.-glucosidase [Gene 75: 73-83 (1989)], yeast .alpha.-glucosidase [Gene 41: 75-84 (1986)], and so on. They are all derived from eukaryotes, and a prokaryote-originated gene useful for industrial production has not been found.
The .alpha.-glucosidase derived from the genus Bacillus is different from the one derived from yeast or animals hitherto known, and has superior heat resistance and wide substrate specificity permitting substantial reaction on maltotetraose, maltopentaose, etc. [Biochimica et Biophysica Acta: 787 281-289 (1984)].
Among strains belonging to the genus Bacillus, however, are those capable of producing .alpha.-amylase concurrently with .alpha.-glucosidase. The .alpha.-glucosidases obtained from those strains contain .alpha.-amylase even after purification, and occasionally cause error in determining amylase in body fluids.